The aim of ÆMINIUM is to study the implications of having a concurrent-by-default programming language. This includes language design, runtime system, performance and software engineering considerations.

Writing concurrent applications is extremely challenging, not only in terms of producing bug-free and maintainable software, but also for enabling developer productivity. In this article we present the Æminium concurrent-by-default programming language. Using Æminium programmers express data dependencies rather than control flow between instructions. Dependencies are expressed using permissions, which are used by the type system to automatically parallelize the application. The Æminium approach provides a modular and composable mechanism for writing concurrent applications, preventing data races in a provable way. This allows programmers to shift their attention from low-level, error-prone reasoning about thread interleaving and synchronization to focus on the core functionality of their applications. We study the semantics of Æminium through μ Æminium, a sound core calculus that leverages permission flow to enable concurrent-by-default execution. After discussing our prototype implementation we present several case studies of our system. Our case studies show up to 6.5X speedup on an eight-core machine when leveraging data group permissions to manage access to shared state, and more than 70% higher throughput in a Web server application.

Linear permissions have been proposed as a lightweight way to specify how an object may be aliased, and whether those aliases allow mutation. Prior work has demonstrated the value of permissions for addressing many software engineering concerns, including information hiding, protocol checking, concurrency, security, and memory management.

Objects model the world, and state is fundamental to a faithful modeling. Engineers use state machines to understand and reason about state transitions, but programming languages provide little support for building software based on state abstractions. We propose Plaid, a language in which objects are modeled not just in terms of classes, but in terms of changing abstract states. Each state may have its own representation, as well as methods that may transition the object into a new state. A formal model precisely defines the semantics of core Plaid constructs such as state transition and trait-like state composition. We evaluate Plaid through a series of examples taken from the Plaid compiler and the standard libraries of Smalltalk and Java. These examples show how Plaid can more closely model state-based designs, enhancing understandability, enhancing dynamic error checking, and providing reuse benefits.